1. Field of the Invention
The present invention relates to an optical coherence tomography apparatus and method.
2. Description of the Related Art
An optical coherence tomography apparatus (hereunder may be referred to as the “OCT apparatus”) is an apparatus for obtaining a tomogram of an object by making use of optical interference. Since an optical coherence tomography apparatus, for example, provides spatial resolution of a micron order and exhibits noninvasiveness, it is actively being studied in the medical field.
An optical coherence tomography apparatus of a swept source type (hereunder may be referred to as the “SS-OCT apparatus”) provides tomogram information at a certain measurement point of an object by using a tunable light source that changes wavelength and by performing scanning using a wavelength of light with which a certain measurement point is illuminated. Since the SS-OCT apparatus does not use a spectroscope that separates interference light, the SS-OCT apparatus has little loss in light quantity. When the SS-OCT apparatus is used to obtain a two-dimensional image, it is necessary to scan a surface of an object with illumination light.
When a two-dimensional image is to be obtained in an existing SS-OCT apparatus, wavelength scanning is started by using a signal (trigger signal) that provides a wavelength scanning start timing, that is, a Fourier transformation start timing. By causing a portion of light from a tunable light source to be divided, transmitting only a particular wavelength by a wavelength filter, and receiving the transmitted light by a photodiode, the trigger signal is generated at a timing in which the light is received by the photodiode, to determine the wavelength scanning start timing. Alternatively, by receiving by the photodiode specularly reflected light from a dispersive element disposed in a tunable light source device, the trigger signal is generated at a timing in which the light is received by the photodiode, to determine the wavelength scanning start timing (refer to Japanese Patent Laid-Open No. 2007-24677.
However, in the above-described methods, in order to obtain a signal that provides the Fourier transformation start timing, a portion of light required to obtain an actual OCT image is wasted, as a result of which the efficiency with which light emitted from the tunable light source is reduced.